[kgm] refactor: convert to enum for dispatch

um_crypto/kgm/src/lib.rs

@@ -1,7 +1,10 @@
 pub mod header;
 pub mod v2;
-mod v3;
+pub mod v3;
 
+use crate::header::Header;
+use crate::v2::DecipherV2;
+use crate::v3::DecipherV3;
 use thiserror::Error;
 
 #[derive(Debug, Error)]
@@ -22,6 +25,37 @@ pub enum KugouError {
     SelfTestFailed,
 }
 
-pub trait Decipher {
-    fn decrypt(&self, buffer: &mut [u8], offset: usize);
+pub enum Decipher {
+    V2(DecipherV2),
+    V3(DecipherV3),
+}
+
+impl Decipher {
+    pub fn new(header: &Header) -> Result<Self, KugouError> {
+        let slot_key: &[u8] = match header.key_slot {
+            1 => b"l,/'",
+            slot => Err(KugouError::UnsupportedKeySlot(slot))?,
+        };
+
+        let decipher = match header.crypto_version {
+            2 => Decipher::V2(DecipherV2::new(header, slot_key)?),
+            3 => Decipher::V3(DecipherV3::new(header, slot_key)?),
+            version => Err(KugouError::UnsupportedCipherVersion(version))?,
+        };
+
+        let mut test_data = header.decrypt_test_data;
+        decipher.decrypt(&mut test_data, 0);
+        if test_data != header.get_challenge_data() {
+            Err(KugouError::SelfTestFailed)?;
+        }
+
+        Ok(decipher)
+    }
+
+    pub fn decrypt<T: AsMut<[u8]> + ?Sized>(&self, buffer: &mut T, offset: usize) {
+        match self {
+            Decipher::V2(decipher) => decipher.decrypt(buffer, offset),
+            Decipher::V3(decipher) => decipher.decrypt(buffer, offset),
+        }
+    }
 }